package com.kylin.type6;

public class SingletonTest06 {
    public static void main(String[] args) {
        System.out.println("使用双重检查完成单例模式");
        Singleton instance1 = Singleton.getInstance();
        Singleton instance2 = Singleton.getInstance();
        System.out.println(instance1 == instance2);
        System.out.println("instance1.hashCode=" + instance1.hashCode());
        System.out.println("instance2.hashCode=" + instance2.hashCode());
    }
}

//懒汉式(线程安全,双重检查)
class Singleton {
    //volatile
    private static volatile Singleton instance;

    private Singleton() {
    }

    //提供一个静态的公有方法,加入双重检查代码，解决线程安全问题，同时解决懒加载问题
    // 懒汉式
    public static Singleton getInstance() {
        if (instance == null) {
            synchronized (Singleton.class) {
                if (instance == null) {
                    instance = new Singleton();
                }
            }
        }
        return instance;
    }
}